Help with MIMOs

Hi everybody!
I got a problem right here making a controller for an exam project. I need to design a wing leveller for an aircraft. It is a MIMO and i
should design it to work as two separated SISO systems. There are two reference variables (inputs) that makes two separate closed loops then the outputs come into one single plant, then two channels right from the single plant go on respective feedbacks. How should i make this thing works? Hope you understand it and please HELP ME! :)
TIA
Metius
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You haven't given all the detail here -- What's the class you're taking? What are the inputs you have available? What are the outputs you need to control, and what are the I/O relationships?
I suspect that you're being asked to control ailerons and elevator, and that your inputs are the pitch and roll outputs of an artificial horizon. I further suspect that you've been given a model where the elevator input has little contribution to roll, and visa-versa.
So look at your plant model -- does input A largely affect output A and input B largely affect output B? If so then can you just treat the cross-axis inputs as disturbances for the purpose of controlling the "direct" channel, and ignore the fact they're in the loop? Try that and see if it works. Don't forget to re-include the cross-axis inputs when you check for stability (smoking holes in the ground can be sooo messy and embarrasing).
I suspect that you were taught this method. If not you were probably given all the bricks that constitute it, and your instructor wants to stretch your mind a little bit. Look back over your notes (or your friends notes, if they'll share) and see if it wasn't mentioned.

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On Fri, 2 Jan 2004 12:20:42 -0800, "Tim Wescott"

Quite right : the inputs are rudder and ailerons control and i must work with yaw and roll angles. They don't seem to affect each other, just the deflections of ailerons and rudder both are inputs of the "aircraft" plant wich has got two identical outputs that lead respectively as feedbacks to their own loop....time to share a scheme, huh? :-)))

As i sad, A and B look quite separated. The initial conditions are : steady state error and washed-out yaw rate = 0 . Dunno what your talking about 'cause MIMOs are part of the second branch of this course and i don't need em until next year :) .

Oh oh...there's nothing about it in my notes.. :-))) I suspect it too, but i would be glad to have some material from where start to taking some good project lines.
Please help me well and you've earned yourself a complete pizza dinner if you come here! I can assure Pizza is good here in Naples. :-)))
Thanks a lot.
Metius
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